The phosphor is utilized in a fluorescent display tube (VFD: vacuum-fluorescent display), a field emission display (FED: Field Emission Display or SED: Surface-Conduction Electron-Emitter Display), a plasma display panel (PDP: Plasma Display Panel), a cathode-ray tube (CRT: Cathode-Ray Tube), a liquid-crystal display backlight (Liquid-Crystal Display Backlight), a white light-emitting diode (LED: Light-Emitting Diode), and so on. In any of these applications, it is necessary to provide the phosphor with energy to excite the phosphor in order to make the phosphor emit fluorescence and the phosphor is excited by an excitation source with high energy such as a vacuum ultraviolet ray, an ultraviolet ray, an electron beam, and blue light so as to emit a visible light ray such as blue light, green light, yellow light, orange light, and red light. However, as a result of the phosphor being exposed to such excitation source, the luminance of the phosphor tends to decrease and a phosphor having little degradation in the brightness is desired. Therefore, a phosphor having an inorganic crystal containing nitrogen in a crystal structure thereof as a host crystal, instead a phosphor such as a silicate phosphor, a phosphate phosphor, a aluminate phosphor, and a sulfide phosphor, has been proposed, as exemplified by a sialon phosphor, an oxynitride phosphor, or a nitride phosphor, which is characterized by low brightness deterioration caused by high energy excitation.
An example of the sialon phosphors is manufactured by a manufacturing process as generally described below. First, silicon nitride (Si3N4), aluminum nitride (AlN), and europium oxide (Eu2O3) are mixed in predetermined molar ratios and the resultant mixture is fired by a hot press method in one atmospheric pressure (0.1 MPa) of nitrogen atmosphere at 1700° C. for one hour (for example, refer to Patent Reference 1). It was reported that α-sialon activated with an Eu ion (Eu2+) manufactured by the above processes had become a phosphor emitting yellow light in a wavelength range of 550 nm to 600 nm if excited by blue light having a wavelength range of 450 to 500 nm. And it is known that an emission wavelength may vary as a ratio of Si to Al or a ratio of oxygen to nitrogen is changed while the α-sialon crystal structure is maintained (for example, refer to Patent References 2 and 3).
As another example of the sialon phosphor, a green phosphor in which β type sialon is activated by Eu2+ is known (refer to Patent Reference 4). It is known that, in the phosphor, an emission wavelength thereof may shift to a shorter wavelength by changing the oxygen content while the crystal structure remains the same (for example, refer to Patent Reference 5). Moreover, it is known that a blue phosphor is to be formed when activated by Ce3+ (for example, refer to Patent Reference 6).
As an example of an oxynitride phosphor, a blue phosphor having a JEM phase (LaAl(Si6-zAlz)N10-zOz) as a host crystal, which is activated by Ce (refer to Patent Reference 7), is known. It is known that, in the phosphor, an emission wavelength thereof may shift to a longer wavelength as well as an excitation wavelength thereof may shift to a longer wavelength by substituting part of La with Ca while the crystal structure remains the same.
As another example of the oxynitride phosphor, a blue phosphor having a La—N crystal La3Si8N11O4 as a host crystal, which is activated by Ce, is known (refer to Patent Reference 8).
As an example of the nitride phosphor, a red phosphor having a crystal of CaAlSiN3 as a host crystal, which is activated by Eu2+, is known (refer to Patent Reference 9). Color rendering properties of a white LED are improved by utilizing this phosphor. A phosphor to which Ce was added as the activating element was reported to be an orange phosphor.
As a host crystal of another nitride phosphor, Ba1Si7N10 or Sr1Si7N10 is known (refer to Non-Patent References 1 and 2). It was reported that a phosphor having Ba1Si7N10 as the host crystal to which Eu2+ was added rendered blue color emission if excited by an ultraviolet ray (refer to Non-Patent Reference 3). Further, it was reported that a phosphor having Sr1Si7N10 as the host crystal to which Ce3+ was added also rendered blue color emission (refer to Patent Reference 10).
Thus, an emission color of the phosphor is determined by a combination of the crystal to act as the host crystal and a metal ion (activating ion) being incorporated into the crystal. Further, the combination of the host crystal and the activating ion determines emission characteristics such as an emission spectrum and an excitation spectrum, chemical stability, and thermal stability such that a phosphor is regarded as another different phosphor when a host crystal thereof or an activating ion thereof is different. Moreover, a material having a different crystal structure is different in the emission characteristics or in the stability because the host crystal is different even if the material has the same chemical composition such that the material is regarded as another different phosphor.
From the described above, it is important to find a host crystal having a new crystal structure in developing a new phosphor and it is possible to propose a new phosphor by activating such a host crystal with an emission-causing metal ion to make the host crystal exhibit luminescence characteristics.